1. Field of the Invention
The present invention is directed to methods of fabricating profiles of varying transmission, more specifically to creating apodized apertures for use in wavefront sensing and the apertures created thereby.
2. Description of Related Art
Hartmann type wavefront sensors measure the spot positions of light diffracted from an array of apertures to determine the shape of an optical wavefront impinging on the aperture array. The original Hartmann sensor used diffraction from hard apertures put into an opaque screen or plate. The demand for high photon efficiency for some applications required the screen be replaced with an array of lenses, forming a Shack-Hartmann wavefront sensor. The advent of micro-optics allowed small high quality arrays to be fabricated.
Currently, Hartmann-type sensors are used for optical meteorology and laser characterization. Lenses for the Shack-Hartmann wavefront sensor have fairly long focal lengths, since this improves the sensitivity of the sensor to phase tilt by increasing the moment arm and spreading the focal spot over many pixels on a CCD which provides better centroid accuracy. These slow, i.e., large f-number, lenses create large diffraction patterns. A diffraction pattern from an individual lens in the detection plane spreads into the area behind neighboring lenses and creates crosstalk. Coherent sources of radiation exacerbate the crosstalk through interference.
Diffraction plays an important role as well in many different types of optical systems. It plays a critical, limiting role in astronomy, for example. With the advent of large, accurate telescopes that are either space-based, or ground-based but using adaptive optics, it is possible to optically resolve planets in orbit around nearby stars. However, these planets would have very little angular separation from the star, and would appear much dimmer. To block the light from the star a small obscuration disk can be placed at an intermediate image plane in the telescope. However, diffraction from the edges of this obscuration would swamp the image of a planet.
Furthermore, diffraction plays a key role in any light propagation or manipulation. As light propagates, either in free space or through a media, both the phase and irradiance distributions affect its state. There are currently a number of means for controlling the phase state of the light. This can be accomplished through a lens, mirror, phase plate or other optical element. In fact, elements can be fabricated to create arbitrary phase states. However, it is currently not possible to control the irradiance state of the light. If both can be controlled together, then the complete E-field of the light has been specified and hence completely arbitrary control of the light at any plane is possible.